Malodors adsorption behavior of metal cation incorporated hydroxyapatite

Several kinds of hydroxyapatites (HAp) prepared by modification of Ca2+-HAp with transition metal (Fe2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) or aluminum (Al3+) ions were evaluated via a gas bag-detection tube method whether they could be used as novel deodorant materials. The samples treated with divalent cation (Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) retained hydroxyapatite structure as well as Ca2+-HAp, whereas those treated with trivalent cation (Al3+ and Fe3+) showed lower crystallinity than Ca2+-HAp. 5-8 wt% cation of the samples was introduced by modification with divalent metal cations, whereas about 40 wt% cation of the samples was introduced with relatively larger surface area and higher content of adsorbed water for trivalent cations. For NH3 gas, modification of Ca2+-HAp with a divalent metal cation enhanced its adsorption ability, and that with a trivalent metal cation resulted in considerable improvement of the ability. On the other hand, modification of Ca2+-HAp with Cu2+ ion gave it remarkable H2S gas adsorption ability in comparison to that with other metal cations. However, adsorption ability for H2S of some polycrystalline powders including Cu2+ was not higher than that of Cu2+-modified HAp. The effect of the incorporated cation on adsorption ability for NH3 molecules may be based not only on a simple Lewis acid-base reaction but also on specific surface area and adsorbed water content, and the effect for H2S molecules based on the specific local electron density around the cation present on/in the material.